Determining the degree of cooling during non-operation of an engine can include determining whether the engine is completely cooled. Determining the degree of cooling during non-operation of an engine can also involve determining duration of continuous non-operation of the engine. Modern vehicles are equipped with units with computation and data storage capabilities, by means of which diagnosis of the vehicle is performed automatically. Such diagnoses are performed to monitor systems in the vehicle, and a main purpose is to reduce emissions. For certain systems and components, for example temperature gauges and the fuel tank system, such diagnosis requires information about the degree of cooling during non-operation of an engine and/or the soak time, i.e. the duration of continuous non-operation of the engine. Again, diagnosis of certain systems and components require that the engine is completely soaked, i.e. completely cooled down.
Known solutions include a timer (a clock) in an electronic control unit, which could be an engine control unit or a central control unit, for measuring the actual soak time of the engine. The soak time is then used for a diagnosis of a type described above. However, not all vehicles are designed with such a soak timer in its engine control system, and more importantly, incorporating a soak timer into an engine control system is costly. Further, a clock does not necessarily provide accurate information about the degree of cooling of the engine. Since the timing information of the clock has to be combined with pre-made assumptions regarding typical cooling characteristics of the engine, there is an element of uncertainty in this solution, since the assumptions may not fully correspond to the characteristics of the engine in use.
In addition to diagnose strategies, modern vehicles with an internal combustion engine engage, by use of electronic engine control systems, strategies for controlling various features of the engine's operation including the air/fuel ratio and/or various engine exhaust system temperatures. It is often necessary for the temperature at locations important in controlling the engine's operation, to be identified at the time the engine is started. By knowing the initial temperature at such locations, the air/fuel ratio, the exhaust system and other features of the engine's operation can be more accurately controlled at the initial stages after the engine is turned on. By determining the soak time, it is possible to in turn determine the temperature at locations important in controlling the engine's operation.
U.S. Pat. No. 5,566,546 discloses a method, in which a soak time is obtained by measuring the temperature of the engine and of the charging air supplied to the engine at the time the engine is turned off and when the engine is restarted. The measured temperature of the engine and of the charging air at the time the engine is turned off is stored in an electronic engine control system. Despite this method being advantageous in view of previous solutions, there is still a need for a simpler way to establish the degree of cooling during non-operation, and the duration of continuous non-operation of the engine, especially, since the solution in U.S. Pat. No. 5,566,546 requires storing measured information during the engine shut-off condition.